Inhomogeneous superconductivity in LuxZr1−xB12 dodecaborides with dynamic charge stripes

Abstract

We have studied the normal and superconductive state characteristics (resistivity, Hall coefficient, heat capacity, and magnetization) of model strongly correlated electronic systems LuxZr1−xB12 with cooperative Jahn-Teller instability of the boron rigid cage and with dynamic charge stripes. It was found that these metals are s-wave dirty limit superconductors with a small mean free path of charge carriers l=5–140Å and with a Cooper pair size changing nonmonotonously in the range 450–4000 Å. The parent ZrB12 and LuB12 borides are type-I superconductors, and Zr to Lu substitution induces a type-I to type-II phase transition providing a variation of the Ginzburg-Landau-Maki parameter in the limits 0.65≤κ1,2≤6. We argue in favor of the two-band scenario of superconductivity in LuxZr1−xB12 with gap values Δ1∼14K and Δ2∼6–8K, with pairing corresponding to strong coupling limit (λe-ph∼1) in the upper band, and to weak coupling (λe-ph∼0.1–0.4) in the lower one. A pseudogap Δps-gap∼60–110K is observed in LuxZr1−xB12 above Tc. We discuss also the possibility of anisotropic single-band superconductivity with stripe-induced both pair breaking and anisotropy, and analyze the origin of a unique enhanced surface superconductivity detected in these model compounds.

Source-reported materials — not catalogue approval

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